1. Field of Invention
The invention relates to electrical energy storing devices and more specifically to energy storing for systems comprising microelectronic integrated circuits with memory.
2. Description of Related Art
Presently, there are three main types of electric supply sources for microelectronic circuits (a chip or a complex electronic system having a determined function):
1) the 110 or 220 V mains from which, after voltage lowering by a transformer, rectifying, filtering and controlling or use of switching devices, a D.C. voltage (usually from 5 to 15 volts) is provided to the microelectronic circuit;
2) the battery which is a self-contained supply source for an electronic device;
3) the rechargeable battery or accumulator, which was usually a lead accumulator and which is presently, generally, in the field of electronic circuit feeding, a cadmium-nickel accumulator.
The mains presents of course the advantage of being a large energy source (in as much as the A.C. mains at 110 or 220 V is reliable) but has however major drawbacks, that is, being cumbersome, weighty, noisy, subject to parasites, and not portable.
The non-rechargeable battery has the drawback of a limited lifetime, a rather poor reliability in an hostile environment, and a high cost.
Therefore, the present trend is to use rechargeable accumulators. Self-contained like a battery, an accumulator solves the problem of the lifetime due to the possibility of recharging, the number of recharges varying according to the electrochemical nature of the accumulator. The problem of reliability is however not solved. Additionally, recharging circuits for rechargeable accumulators ape generally relatively complex and generate an electromagnetic noise. Additionally, if they are disposed inside the system to be supplied, they are cumbersome and take an important surface on a printed circuit board provided in the system.